1. Field of the Invention
The present invention relates to a novel hydrazone compound useful as a charge transfer material in an electrophotographic element, which is expressed by the general formula ##STR3## (wherein Ar represents substituted or non-substituted naphthyl group, anthryl group, styryl group, pyridyl group, thienyl group, furyl group or carbazolyl group.);
the process for manufacturing thereof; and the utilization of said compound or analogues thereof for electrophotographic elements.
2. Description of the Prior Art
As conventional photoconductive materials for photosensitive elements useful in electrophotographic systems, there are known inorganic materials such as selenium, cadmium sulfide, zinc oxide and the like. The "electrophotographic system" herein is an image-forming method which generally comprises: charging a photosensitive element with electricity by means of corona discharge in the dark, subsequently imagewise exposing the element to light; selectively dispelling the electric charge of only the light-exposed portions of the element to thereby obtain an electrostatic latent image; and rendering visible this latent image area through a developing means using electroscopic fine particles called toner consisting of a coloring agent such as dyes, pigments, etc. and a binder such as high molecular substances to thereby form an image. To mention the fundamental characteristics required for the photosensitive element in such an electrophotographic method, (1) it should be capable of being charged with electricity to a suitable degree of potential in the dark, (2) it allows little dissipation of the electric charge thereof in the dark, and (3) it should be capable of rapidly dissipating the electric charge thereof when subjected to radiation of light.
The above mentioned conventional inorganic photosensitive elements admittedly have many advantages, but, on the other hand, they have various deficiencies. Accordingly, there have recently been proposed organic photosensitive elements utilizing many kinds of organic materials, and some of them have been put to practical use. Among others, a photosensitive element comprising a material which absorbs light and generates charge carriers (hereinafter called a charge carrier generating material) and a material which accepts charge carriers and transfers them (hereinafter called a charge transfer material) is known to be capable of providing an unprecedentedly high sensitivity because it permits a wide range of selection of materials suitable for every function compared with the photosensitive elements designed for performing the generation of charge carriers and the transfer of charge carriers by means of one and the same material. To mention the requirements for the materials to be used in this kind of photosensitive element, as to said charge carrier generating material, it should be capable of absorbing a desired light and generating charge carriers; it should be capable of displaying a high efficiency in generating charge carriers; it should be easy to treat for preparation of the photosensitive element; and so forth, while as to said charge transfer material, it should be capable of readily accepting charge carriers from the charge carrier generating material; it should permit rapid transfer of charge carriers; it should not show absorption of light in the photosensitive region of the charge carrier generating material; and so forth. Further, it is especially to be noted that the charge transfer material suitable for use in the photosensitive element varies with the charge carrier generating material employed. When the combination of the charge carrier generating material with the charge transfer material is not appropriate, the potential of charged electricity in the dark fails to be sufficient, the resulting image is of low density because of insufficient dissipation of electric charge at the time of radiation of light, and the ground gets stained. Generally speaking, a photosensitive element which has a high potential of charged electricity in the dark tends to be poor in dissipation of the electric charge, while one which shows good dissipation of the electric charge tends to have a low potential of charged electricity, and this tendency varies with the kind of the charge carrier generating material and also the kind of the charge transfer material employed. For practical purposes, an appropriate combination of the charge carrier generating material and the charge transfer material is so selected as to realize dissipation of the charge to such a degree as will not cause stains of the ground and to attain a potential charged to such a degree as will bring about sufficient image densities.
As the above mentioned charge carrier generating materials, there have been proposed a great many substances. To cite especially effective substances, there are CI Pigment Blue 25 (Color Index 21180), azo pigment having carbazole skeleton (as disclosed in Japanese Laid-open Patent Application No. 95033/1978), azo pigment having triphenylamine skeleton, azo pigment having styrylstilbene skeleton (as disclosed in Japanese Laid-open Patent Application No. 13344/1978), azo pigment having diphenyloxadiazole skeleton (as disclosed in Japanese Laid-open Patent Application No. 12742/1979), azo pigment having fluorenone skeleton (as disclosed in Japanese Laid-open Patent Application No. 22834/1979), etc. However, for the foregoing reasons, the charge transfer materials suitable to these charge carrier generating materials are different from one another.